P1327: INHIBITING TELOMERIC DNA DAMAGE RESPONSE AS A NEW THERAPEUTIC STRATEGY TO REJUVENATE THE AGEING HEMATOPOIETIC SYSTEM
Authors: Alessia Oppezzo, Sara Sepe, Francesca Rossiello, Anastasia Conti, Eugenia Marinelli, Sara Boggio, Alessia DI Lillo, Ilaria Rosso, Sara Tavella, Valentina Matti, Giada Cicio, Valeria Cancila, Alexandra Mancheno-Ferris, Giorgio Bertolazzi, Fabio Iannelli, Raffaella DI Micco, Claudio Tripodo, Fabrizio D’adda DI Fagagna
Journal: HemaSphere (2023)

Topic: 23. Hematopoiesis, stem cells and microenvironment Background: As we age, we become highly prone to suffer from age-dependent hematological diseases including anemia, myeloid and lymphoid leukemias, autoimmunity and a series of changes known as “immunosenescence’, including the involution of primary lymphoid organs, the contraction of the immune repertoire, a progressive lineage skewing towards the myeloid lineage and a low-grade pro-inflammatory status. Our group has reported that dysfunctional telomeres are actively transcribed to generate telomeric non-coding RNAs (tncRNAs) which are essential to recruit DDR factors at damaged telomeres, thus fueling DDR and causing cellular senescence initiation and maintenance. Sequence-specific telomeric antisense oligonucleotides (tASOs) target these tncRNAs and effectively inhibit DDR activation in cultured cells (Rossiello, Nat Commun, 2017) and improve the progeroid pathological phenotype of a mouse model of Hutchinson-Gilford progeria syndrome (HGPS) (Aguado, Nat Commun, 2019), validating tASOs as a promising therapeutic agent for HGPS and potentially for other diseases caused by telomeric dysfunction. A well-validated animal model to study telomere dysfunction and aging is the telomerase-deficient (Terc-/-) mouse model, characterized by accelerated telomere shortening and dysfunction and recapitulating several features of immunosenescence: immune system reactivity reduction, decreased long term renewal of hematopoietic stem cells and lymphocytes numbers, and increased neutrophil count. Aims: The aim of our project is to demonstrate the efficacy of tASOs in inhibiting DDR in vivo with the final aim of long-term beneficial effects on the hematopoietic/immune system. Methods:Terc-/- mice were treated at a young age (3-month-old) with tASOs (15 mg/kg) twice a week for four weeks and their effects on the hematopoietic/immune system were assessed up to 9 months after treatment. Hematopoietic Stem and Progenitor Cells (HSPCs) fitness, immune cell composition of hematopoietic organs and DDR by flow cytometry and immunohistochemistry and RNAseq analysis to explore the signaling pathways affected by tASOs treatment were performed. Results: Our tASOs administration protocol on premature-aging Terc-/- mice shows effects up to 9 months after the treatment, with reduced DDR activation in mice tissues and improved overall pathological score in the bone marrow (BM) and spleen. RNAseq analysis shows that tASOs restore altered biological pathways, including the inflammatory response. In addition, tASOs treatment improves the dysfunctional hematopoietic/immune phenotype of Terc-/- mice by improving the colony forming ability of BM-derived HSPCs, by restoring the normal cell composition of BM and spleen, including the myeloid-to-erythroid ratio in the BM and by reverting extramedullary hematopoiesis in the spleen. In addition, tASOs were able to improve survival in an additional distinct aplastic anemia mouse model and, most importantly, were effective in increasing the ex vivo colony forming ability of human CD34+ cells from aged donors, validating their beneficial effects not only on the hematopoietic system in a different mouse model, but also on human cells. Summary/Conclusion: These results indicate that inhibiting DDR at damaged telomeres in vivo in mouse models and ex vivo in human stem cells can have beneficial effects on the immunosenescent phenotype, by counteracting not only the hematopoietic/immune impairment but also diminishing the inflammation typical of advanced age. By improving these features of aging, tASOs treatment could be employed as a novel therapeutic strategy to rejuvenate the ageing hematopoietic system. Keywords: Aging, Senescence, Telomere, DNA damage